This research involves two projects: (1) electron transfer reactions in mono- and binuclear metal complex systems; (2) preparation and investigation of structural, electronic, and reactivity properties of Fe(II, III) porphyrins with axial thiolate ligands. In (1) the effects of electronic and structural properties of Cu(I,II) redox potentials are under study by use of a large variety of complexes with different dimer groups and constrained planar and non-planar stereochemistry. This work is directed toward an interpretation of the exceptionally high potentials found in certain Cu proteins. Binuclear Fe(III) complexes of the type (Fe2S2(SR)2 (SR')2)2-, synthetic analogs of 2-Fe ferredoxin protein active sites, undergo two one-electron reductions at potentials dependent on R and R'. The extent of electron delocalization is being investigated as a function of the difference in redox potentials of the two metal sites in order to provide information necessary to the interpretation of trapped valences found in the reduced proteins. In (2) a variety of porphyrin complexes have been prepared containing an axial thiolate ligand, and electronic, structural, and reactivity properties are under investigation in order to ascertain whether axial cysteinyl ligands are present in the cytochrome P-450 hydroxylase enzymes.